Type 2 diabetes (T2DM) develops in 50% of women with gestational diabetes (GDM) within 5 years after delivery. Although randomized trials have shown that diet and physical activity (PA) reduce the risk of T2DM, no lifestyle interventions have been translated for use in pregnant and early postpartum women with GDM. The primary aim of the study is to implement and evaluate among women with GDM an intervention of diet and PA that starts during pregnancy and continues after pregnancy with the primary goals of a) reaching prepregnancy weight if women had normal weight prior to pregnancy; or b) reaching 5% reduction of the prepregnancy body weight if women were overweight or obese prior to pregnancy. Secondary outcomes are postpartum diet (percent calories from fat), time spent in PA and plasma glucose levels. All participants will have GDM (by plasma glucose levels during a 100-g, 3-h OGTT) from a large population (62% from ethnic minority groups) receiving medical care at Kaiser. At study entry (< 32 weeks' gestation) eligible women will be randomly assigned to lifestyle intervention or usual medical care (170 women in each group). Intervention women will be also taught about their diabetes risk and how to prevent it. Targets for intervention during pregnancy (Phase I) are to help women comply with the Institute of Medicine guidelines for weight gain by following recommendations for diet and PA. Phase I will be delivered through 1 individual in-person session and 3 telephone counseling contacts. After pregnancy (Phase II), starting from 6 weeks postpartum, targets for intervention are to help women meet their postpartum weight goals. Phase II will be delivered through 3 in-person sessions and 13 telephone counseling contacts. The maintenance period (Phase III) begins at 9 months and will end at 24 months postpartum and will include 8 mailed tailored reminders. Measurements will be collected at study entry and at 6-week, 8-month, 12-month, 18-month and 24-month postpartum. Data analyses will be by intent-to-treat. Tertiary aims address psychosocial modeling, within trial cost- effectiveness analysis and evaluation of the intervention for possible adoption into Kaiser standard care. This study takes advantage of the Kaiser database that allows "real-time" identification of GDM women, providing considerable efficiency in time and costs. The study proposes to, use a telehealth intervention that is effective in women with infants and has the potential to be translatable to many other clinical settings. [unreadable] [unreadable]